IV Fluids and Fluid Balance: cram pack

Formula sheets, the key method steps for every topic and 4 practice problems, with full solutions at the back.

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1Formulas and methods

IV fluids & fluid balance

Holliday–Segar per hour
4 mL/kg (first 10 kg) + 2 mL/kg (next 10 kg) + 1 mL/kg (each kg above 20)
Holliday–Segar per day
100 / 50 / 20 mL/kg for the same bands
Fluid balance
intake − output
Ice chips
count as half their volume
Urine output
mL/kg/h = mL / (kg × h)
Infusion time
time (h) = volume left (mL) / rate (mL/h)
Volume infused
mL = rate × time

IV infusion rates

Pump rate
mL/h = volume (mL)/time (h)
Drip rate
drops/min = volume (mL) × drop factor / time (min)
Infusion time
time (h) = volume (mL)/rate (mL/h)

Method

  1. Pump rate in mL/h: volume divided by time in hours.
  2. Drip rate in drops/min: volume × drop factor divided by time in minutes.
  3. For time remaining: volume left divided by the rate.
  4. Round as the question or the equipment requires.

2Practice problems

1.IV fluids & fluid balanceMedium
IntakeOutput8-hour shifttea150 mLjelly100 mLIV infusion100 mL/h × 8 hIV antibiotic1 × 50 mLurine150 mLurine150 mLurine325 mL

Practice exercise (made-up values, not clinical guidance). The record shows a patient's intake and output for one 8-hour shift. The IV infusion ran at the rate shown for the whole shift. Find the fluid balance B = intake − output in mL (a negative answer means a net loss).

tea: 150 mLjelly: 100 mLIV infusion: 100 mL/h × 8 hIV antibiotic: 1 × 50 mLurine: 150 mLurine: 150 mLurine: 325 mL
B = mL
2.IV fluids & fluid balanceHard
500 mL150 mL infused100 mL/h14:00t = ? h

Practice exercise (made-up values, not clinical guidance). A 500 mL bag runs by pump at 100 mL/h. At 14:00, 150 mL have already been infused. How many hours t until the bag is empty? Round to one decimal place.

500 mL150 mL infused100 mL/h
t = h
3.IV infusion ratesMedium
V = ?15 gtt/mL20 gtt/min2 h

A drip runs at 20 gtt/min through a set of 15 gtt/mL. How many millilitres V does the patient receive in 2 hours?

20 gtt/min15 gtt/mL2 h
V = mL
4.IV infusion ratesHard
900 mL15 gtt/mL50 gtt/mint = ? h

A drip runs at 50 gtt/min through a set of 15 gtt/mL. There are 900 mL left in the bag. How many hours t until it is empty?

50 gtt/min15 gtt/mL900 mL
t = h

3Solutions

1.IV fluids & fluid balance

Answer: B = 475 mL

Intake and output: intake counts everything that goes in (oral fluids, IV infusions, IV medications and flushes, tube feeds); ice chips count as half their volume. Output counts urine, drains, vomit and other losses. Balance = total intake − total output; a negative balance is a net loss. The numbers are for practice only; at the bedside always follow local protocols and have high-risk doses double-checked.

Total intake

oral: 150 + 100 = 250 mL
IV infusion: 100·8 = 800 mL
IV antibiotic: 1·50 = 50 mL
total intake = 1100 mL

Total output

150 + 150 + 325 = 625 mL

Balance

B = 1100 − 625 = 475 mL

Answer

B = 475 mL

Positive: more fluid went in than came out.

2.IV fluids & fluid balance

Answer: t = 3.5 h

Infusion time: time (h) = volume to infuse (mL)/rate (mL/h); use the volume still left in the bag, not the bag size. Volume infused = rate × time. Convert decimal hours to hours and minutes with the fraction × 60 (0.5 h = 30 min, not 50 min). The numbers are for practice only; at the bedside always follow local protocols and have high-risk doses double-checked.

Volume left

500 − 150 = 350 mL

Time

t = 350/100 = 3.5 h

Answer

t = 3.5 h

That is about 3 h 30 min, so the bag runs out at about 17:30.

3.IV infusion rates

Answer: V = 160 mL

Infusion rates: a pump is set in mL/h = volume/time in hours. A gravity drip is counted in drops per minute: gtt/min = volume (mL) × drop factor (gtt/mL)/time (min). The drop factor is printed on the tubing package: macrodrip sets deliver 10, 15 or 20 gtt/mL (blood sets often 10 gtt/mL in the US, 15 in the UK) and microdrip sets 60 gtt/mL. Always use the drop factor the question or package gives.

Rate in mL/h

20·60/15 = 80 mL/h

Volume

V = 80·2 = 160 mL

Answer

V = 160 mL
4.IV infusion rates

Answer: t = 4.5 h

Infusion rates: a pump is set in mL/h = volume/time in hours. A gravity drip is counted in drops per minute: gtt/min = volume (mL) × drop factor (gtt/mL)/time (min). The drop factor is printed on the tubing package: macrodrip sets deliver 10, 15 or 20 gtt/mL (blood sets often 10 gtt/mL in the US, 15 in the UK) and microdrip sets 60 gtt/mL. Always use the drop factor the question or package gives.

Rate in mL/h

50·60/15 = 200 mL/h

Time left

t = 900/200 = 4.5 h

Answer

t = 4.5 h

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